One-Pot Synthesis of Spirocyclic or Fused Pyrazoles from Cyclic

23 Aug 2017 - Yue Yu, Yang Chen, Wei Huang, Wanqing Wu, and Huanfeng Jiang. Key Laboratory of Functional Molecular Engineering of Guangdong ...
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One-Pot Synthesis of Spirocyclic or Fused Pyrazoles from Cyclic Ketones: Calcium Carbide as the Carbon Source in Ring Expansion Yue Yu, Yang Chen, Wei Huang, Wanqing Wu,* and Huanfeng Jiang* Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China S Supporting Information *

ABSTRACT: N-Tosylhydrazones generated in situ from cyclic ketones smoothly underwent a [3 + 2] cycloaddition to afford saturated spirocyclic pyrazoles and further transformed to the fused analogues via a ring expansion in certain cases. An inexpensive and renewable resource, calcium carbide, was utilized as the carbon source in the ring expansion. The salient features of this reaction include widely available starting materials, convenient one-pot/two-step procedure, great efficiency, and high regioselectivity. Remarkably, this reaction underwent a [1,5]-sigmatropic rearrangement process, which was supported by deuterium-labeling experiments.

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INTRODUCTION Owing to their convenient accessibility and structural diversity, cycloalkanone derivatives have been widely used as raw materials for many total syntheses of natural products and bioactive molecules.1,2 Ring expansion reactions of cycloalkanones rank among the most strategically useful in the steps of these syntheses because many natural products consist of unavailable polycyclic networks. To date, there have been various methods developed for the ring expansion of cycloalkanones,3 some of which have even become name reactions. For examples, the Lewis acid-catalyzed addition of αdiazoacetates or diazoalkanes to cyclohexanones has been known for more than half a century as a practical strategy to synthesize seven-membered carbocyclic ketones through the Tiffeneau−Demjanov rearrangement intermediates (Scheme 1a).4 Another well-known and efficient method is the Dowd− Beckwith ring expansion reaction, in which the 2-oxocyclohexanecarboxylate compounds are transformed to medium-sized ring cyclic ketones. However, this process requires the addition of toxic or explosive reagents such as AIBN and Bu3SnH, and environmentally unfriendly haloalkane substrates are used as the carbon source (Scheme 1b).5 To expand the richness of green ring expansion reactions, we searched for other atom-economical and easy-to-obtain carbon sources. It is known that calcium carbide (CaC2) is thought to be a promising candidate for a safer and more inexpensive alternative to acetylene gas that has become an important basic organic chemical raw material.6 Therefore, the conversions of CaC2 to acetylene-derived compounds have received continuing attention in these years owing to their potential to the preparation of 3-substituted or 3,4-disubstituted 1H-pyrazoles in industry field by using CaC2 as the source.7 The reaction © 2017 American Chemical Society

Scheme 1. Transition-Metal-Free Ring Expansion Reactions of Cyclic Ketones

pathways have been clarified that the 3H-pyrazole intermediates were involved and spontaneously rearranged to the final products. On the basis of this work and Valdés’s report,8 we envisaged that the 3H-pyrazole intermediate could be stably isolated as product by using symmetrical cyclic ketones as substrates. In addition, asymmetrical cyclic ketones would undergo the [3 + 2] cycloaddition/[1,5] rearrangement sequence to give the fused pyrazoles with expansion of the carbocyclic ring. In this context, we report herein a new method Received: June 16, 2017 Published: August 23, 2017 9479

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

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The Journal of Organic Chemistry

With the optimized reaction conditions in hand, we turned our attention to the generality of this transformation (Table 2).

for utilizing CaC2 as both an acetylide source in the [3 + 2] annulation and the carbon source in ring expansion to synthesize spirocyclic or fused pyrazoles (Scheme 1c). Such saturated polycyclic pyrazole motifs were prevalent structural elements in numerous compounds of significant biological/ medicinal value for the applications in dyes, agrochemicals, and pharmaceuticals.8−11 However, their preparations were typically challenging to achieve directly by using conventional methods.

Table 2. Substrate Scope for the Synthesis of Spirocyclic Pyrazolesa

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RESULTS AND DISCUSSION At the outset of our studies, we investigated this reaction for the synthesis of spiro-heterocycles from 4-phenyl-cyclohexanone (1b) and calcium carbide. The condensation reaction between ketones and tosylhydrazide can easily afford N-tosylhydrazones in situ without the need for chromatographic purification.12 Therefore, a mixture of 1b and tosylhydrazide was first stirred at 70 °C for 2 h in methanol, followed by removal of the solvent. The remaining crude mixture was then treated with excessive amounts of CaC2, H2O, and equivalent amounts of bases in appropriate solvents. To our delight, when the reaction was performed in DMSO at 80 °C for 6 h with the addition of Cs2CO3, the desired spirocyclic pyrazole 3b was obtained in 51% isolated yield (Table 1, entry 1). Subsequent screening of Table 1. Optimization of Reaction Conditionsa

a Reaction conditions: (1) 1 (0.5 mmol), TsNHNH2 (0.5 mmol), MeOH (2 mL) at 70 °C for 2 h; (2) CaC2 (2 mmol), base (0.5 mmol), H2O (2.5 mmol), and 2.0 mL DMSO at 110 °C for 6 h. bNVinyl pyrazole product 3i′ was detected in 13% yield. cN-Vinyl pyrazole product 3j′ was detected in 16% yield. d90 °C.

entry

base

solvent

T (°C)

yieldb(%)

1 2 3 4 5 6 7 8 9 10 11 12 13

Cs2CO3 K2CO3 KOH t-BuOLi MeONa Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3

DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMF 1,4-dioxane DMA CH3CN toluene

80 80 80 80 80 100 110 120 110 110 110 110 110

54 (51)c 35 29 11 46 79 92 (87)c 90 63 86 65 trace trace

Initially, N-tosylhydrazones generated from cyclohexanone and 4-substituted cyclohexanones were found to undergo [3 + 2] annulations with CaC2 to give the corresponding spiroheterocycles 3a−3c in 73−87% yields. Pleasingly, a series of 6-membered saturated oxygen-, sulfur-, and nitrogen-containing heterocyclic ketones were also suitable substrates for this cyclization so that the target products 3d−3h were isolated in 61−89% yields. Concerning the cycloalkanone ring size, cycloheptanone, cyclooctanone, and adamantanone were next investigated, and the corresponding products (3i−3k) were obtained in moderate to good yields. Notably, when cyclopentanone 1l was examined, a 6-membered fused pyrazole product 3l was afforded in 56% yield, while the spirocyclic one was not detected. We supposed that spontaneous rearrangement in this manner might occur based on the angle strain in the spirocyclic intermediate. Moreover, the temperature of this transformation should not be more than 100 °C; otherwise, 3l would further react with another equivalent of acetylene via nucleophilic addition to form a N-vinyl pyrazole product instead. As for other cycloalkanones, cyclobutanone was found to be in similar situation with cyclopentanone, albeit with too low of a yield wherein the product was detected only by crude 1 H NMR. The spirocyclic substrates that spontaneously rearranged to the fused analogues prompted us to examine the synthesis of fused pyrazoles 4 directly from their parent cyclic ketones. In addition to the angle strain, a rich electron density adjacent to the carbonyl moiety was also anticipated to be an important influence factor for the expansion of the carbocyclic ring in this reaction. Therefore, various examples were tested under similar reaction conditions with a lower temperature, as shown in Table 3. Indeed, [3 + 2] annulations between CaC2 and a series

a

Reaction conditions: (1) 1 (0.5 mmol), TsNHNH2 (0.5 mmol), MeOH (2 mL) at 70 °C for 2 h; (2) CaC2 (2 mmol), base (0.5 mmol), H2O (2.5 mmol), and 2.0 mL solvent under heating for 6 h. b GC yield with n-dodecane as internal standard. cNumber in parentheses is the yield of isolated product.

other bases such as K2CO3, KOH, t-BuOLi, or MeONa did not improve the yield (Table 1, entries 2−5). Significantly, increasing the reaction temperature had a positive effect on the yield. The optimal temperature was found to be 110 °C, affording the target product 3b in 87% isolated yield (Table 1, entries 6−8). Different types of solvents were then investigated, but no superior results were obtained (Table 1, entries 9−13). Furthermore, the molecular structure of 3b was unambiguously determined by X-ray crystallographic analysis (see Supporting Information for details). 9480

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

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The Journal of Organic Chemistry Table 3. Substrate Scope of the Cyclization/Ring Expansiona

Scheme 2. Further Modification on Biologically Active Molecules

Scheme 3. Gram-Scale Experiments

a Reaction conditions: (1) 2 (0.5 mmol), TsNHNH2 (0.5 mmol), MeOH (2 mL) at 70 °C for 2 h; (2) CaC2 (2 mmol), base (0.5 mmol), H2O (2.5 mmol), and 2.0 mL DMSO at 80 °C for 6 h.

addition of Cs2CO3 and D2O. It was found that the reaction afforded the corresponding deuterated pyrazole [D2]-4m in 80% yield with 97% D (Scheme 4, eq 1). To confirm whether

of N-tosylhydrazones generated from 5-membered cyclic ketenes or benzo ketones proceeded smoothly to give the corresponding pyrazoles fused to a six-membered ring in moderate to good yields (4a−4g). Owing to the rich electron density of vinyl and aryl groups, the [1,5]-sigmatropic rearrangement took place again in a regioselective manner, thus giving rise exclusively to the ring-expanded pyrazoles. Furthermore, a range of 6- and 7-membered saturated cyclic ketenes or benzo ketones were then investigated in the reaction as well, and the corresponding 7- or 8-membered products were generated in 50−88% yields (4h−4q). In general, ketones with electron-donating substituents on the phenyl ring furnished the desired products in yields higher than those with electron-neutral or electron-withdrawing groups. We then applied the present protocol to the functionalization of two biologically active molecules. Under the standard conditions, (−)-Carvone 5 and (+)-Nootkatone 7 could undergo further modification smoothly, and the corresponding pyrazoles 6 and 8 were successfully obtained in moderate yields (Scheme 2). The practicality of this ring-expansion reaction using calcium carbide as a one-carbon unit should lead to potential utilities in the synthesis of valuable polycyclic pyrazole derivatives. To validate the potential industrial applications of this strategy, two scale-up experiments were then carried out for 4phenyl-cyclohexanone (1b) and 4,4-dimethylcyclohex-2-enone (2i) (Scheme 3). The two reactions afforded the corresponding spirocyclic pyrazole 3b or fused pyrazole 4i in gram scale, albeit in diminished yields as compared with the small-scale experiments (see Supporting Information for details). To cast some light on the mechanism details for our reaction, deuterium-labeling experiments were conducted. Initially, the reaction of CaC2 and N-tosylhydrazone generated in situ from 2m was performed in dry DMSO at 80 °C for 6 h with the

Scheme 4. Deuterium-Labeling Experiments

the deuteration occurred before or after the cyclization, we tested the reaction of pyrazole 4m under the standard conditions in the presence of Cs2CO3 and D2O, and the deuterated product [D2]-4m was not detected, which suggested that the deuteration occurred before the [3 + 2] cyclization (Scheme 4, eq 2). In view of the structure of [D2]-4m and our previous works,7 we deduced that the deuterium atom on N1 was shifted from C4 of the pyrazole ring through multiple [1,5]-H shifts during the process of aromatic isomerization. Before that, a migration of phenyl group from C3 to C4 through [1,5]-sigmatropic rearrangement should occur. We also tried to cultivate single crystals of pyrazoles 4, but no direct experimental result was obtained. We supposed that, due to the prototropic tautomerism of 1H-pyrazoles, the characters of 4 are either oils or amorphous powders. Because the migrational principles of [1,5]-sigmatropic rearrangement are clear, the structures of 4 are considered credible. 9481

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

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mass spectrometer (LCMS-IT-TOF). IR spectra were obtained either as potassium bromide pellets or as liquid films between two potassium bromide pellets with a Bruker TENSOR 27 spectrometer. Melting points were determined with a Büchi Melting Point B-545 instrument. General Procedure for the Preparation of 3 and 4. In a Schlenk tube, a mixture of cyclic ketone (0.5 mmol) and tosylhydrazide (0.5 mmol) was stirred at 70 °C for 2 h in methanol (3 mL), followed by removal of the solvent in vacuo. The remaining crude mixture was then treated with CaC2 (2 mmol), Cs2CO3 (0.5 mmol), H2O (2.5 mmol, added by using a microliter syringe), and DMSO (2 mL). The mixture was stirred at 110 or 80 °C for 6 h. After completion of the reaction (monitored by TLC), water (10 mL) was added to the reaction mixture, and the resulting mixture was extracted with ethyl acetate. The combined organic layers were then dried over MgSO4, filtered, and then concentrated in vacuo. The residue was purified by flash chromatography on silica gel to give 3 or 4. Procedure for the Preparation of 3b or 4i on a Gram Scale. In a 200 mL round-bottom flask with a reflux condenser, a mixture of 1b (1.74 g, 10 mmol)/2i (1.24 g, 10 mmol) and tosylhydrazide (1.86 g, 10 mmol) was first stirred at 70 °C for 2 h in methanol, followed by removal of the solvent. The remaining crude mixture was then treated with CaC2 (2.56 g, 40 mmol), Cs2CO3 (3.26 g, 10 mmol) and H2O (0.9 mL, 50 mmol) in DMSO (40 mL). The flask was then sealed with an uninflated balloon and the mixture was stirred at 110 °C/80 °C for 6 h. After completion of the reaction (monitored by TLC), water (3 × 100 mL) was added to the reaction mixture, and the resulting mixture was extracted with ethyl acetate 3 times. The combined organic layers were then dried over MgSO4, filtered, and then concentrated in vacuo. The residue was purified by flash chromatography on silica gel to give 3b as a brown solid or 4i as a yellow oil. 1,2-Diazaspiro[4.5]deca-1,3-diene (3a). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a black oil (57.9 mg, 85%); IR (KBr): 2930, 2858, 1670, 1444, 1048 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.56 (s, 1H), 7.13 (s, 1H), 2.08−2.01 (m, 2H), 1.92 (t, J = 11.2 Hz, 2H), 1.73−1.53 (m, 4H), 1.34−1.26 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 145.5, 142.6, 97.4, 30.5, 25.3, 24.5; MS (EI, 70 eV) m/z: 136.25, 108.22, 94.20, 84.04; HRMS ESI (m/z): calcd for C8H13N2 [M + H]+: 137.1073, found: 137.1074. 8-Phenyl-1,2-diazaspiro[4.5]deca-1,3-diene (3b). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a brown crystalline solid (92.3 mg, 87%), mp 110.5−111.9 °C; IR (KBr): 3081, 2929, 1700, 1438, 690 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.60 (s, 1H), 7.35 (t, J = 9.5 Hz, 4H), 7.22 (t, J = 6.9 Hz, 1H), 6.92 (s, 1H), 2.81 (t, J = 12.2 Hz, 1H), 2.54−2.42 (m, 2H), 2.06 (dd, J = 22.6, 12.3 Hz, 4H), 1.28 (d, J = 13.9 Hz, 2H); 13 C NMR (100 MHz, CDCl3) δ 147.7, 146.5, 142.2, 128.3, 126.8, 126.1, 95.2, 43.5, 31.6, 31.4; MS (EI, 70 eV) m/z: 212.28, 134.25, 108.20, 94.21; HRMS ESI (m/z): calcd for C14H16N2Na [M + Na]+: 235.1206, found: 235.1210. 9,12-Dioxaspiro-1,2-diazaspiro[4.5]deca-1,3-diene (3c). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown crystalline solid (70.9 mg, 73%), mp 127.8−128.9 °C; IR (KBr): 3740, 3087, 1739, 1259, 952 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.61 (s, 1H), 7.07 (s, 1H), 4.10−3.97 (m, 4H), 2.30 (t, J = 8.4 Hz, 2H), 1.88−1.70 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 145.5, 142.9, 108.0, 64.5, 64.5, 33.4, 28.6; MS (EI, 70 eV) m/z: 194.26, 149.22, 107.20, 87.17; HRMS ESI (m/z): calcd for C10H14N2NaO2 [M + Na]+: 217.0947, found: 217.0950. 8-Oxa-1,2-diazaspiro[4.5]deca-1,3-diene (3d). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a brown oil (57.4 mg, 83%); IR (KBr): 3738, 2928, 1744, 1524, 1038, 883 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.72−7.59 (m, 1H), 7.14−7.00 (m, 1H), 4.34−4.23 (m, 2H), 3.94−3.85 (m, 2H), 1.79−1.65 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 144.6, 143.4, 93.8, 65.8, 30.0; MS (EI, 70 eV) m/z: 138.36,

On the basis of the results of deuterium-labeling experiments and previous works,7,8a we tentatively proposed the reaction mechanism as outlined in Scheme 5. Initially, in the presence of Scheme 5. Possible Mechanism

Cs2CO3, the cesium salt A was afforded by the deprotonation of N-tosylhydrazone 1′. In one possible way, reactive diazo compound B was rapidly formed under the action of the base, followed by a [3 + 2] cycloaddition with [D2]-acetylene gas, affording deuterated spirocyclic pyrazole [D2]-3 (Path I). Another possibility is that nucleophilic addition of the counter N-anion of intermediate A to [D2]-acetylene gas followed by the elimination of Ts anion and cesium ion led to the spirocyclic product [D2]-3 (Path II). The reactions of 6-, 7-, or 8-membered heterocyclic ketones resulted in spirocyclic products which would not spontaneously rearrange. While for 4 or 5-membered cyclic ketones with strong angle strain or substrates with rich electron density adjacent to the carbonyl moiety, the nonaromatic spirocyclic pyrazole [D2]-3 has a trend to isomerize to the aromatic fused analogues. Thus, a spontaneous [1,5]-sigmatropic rearrangement from [D2]-3 to E through the transition state D must be favored, and the subsequent multiple [1,5]-D shifts gave the final product [D2]4. In summary, we present a convenient one-pot/two-step procedure for transition-metal-free coupling between calcium carbide and N-tosylhydrazones generated in situ from cyclic ketones, affording saturated spirocyclic pyrazoles via [3 + 2] cycloadditions. In certain cases, the spirocyclic pyrazoles could undergo a ring expansion to give the fused analogues, in which calcium carbide was used as the carbon source. In addition, deuterium-labeling experiments were conducted to clarify the reaction pathway that multiple [1,5]-sigmatropic rearrangements were involved in the transformation. From a synthetic point of view, this ring-expanded reaction should lead to great utilities in the formation of biologically active pyrazole scaffolds.

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EXPERIMENTAL SECTION

General Methods. 1H and 13C NMR spectra were recorded using a Bruker DRX-400 spectrometer using CDCl3 as solvent. The chemical shifts are referenced to signals at 7.26 and 77.0 ppm, respectively. Mass spectra were recorded on a Thermo Scientific ISQ gas chromatograph−mass spectrometer. HRMS was carried out on a high-resolution 9482

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

Article

The Journal of Organic Chemistry 109.22, 95.17, 79.17; HRMS ESI (m/z): calcd for C7H11N2O [M + H]+: 139.0866, found: 139.0865. 8-Thia-1,2-diazaspiro[4.5]deca-1,3-diene (3e). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a brown amorphous solid (68.6 mg, 89%), mp 142.7−144.4 °C; IR (KBr): 3740, 3089, 2924, 1427, 1254, 913 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.65 (d, J = 3.2 Hz, 1H), 7.09 (d, J = 3.2 Hz, 1H), 3.33−3.23 (m, 2H), 2.79−2.71 (m, 2H), 2.01− 1.94 (m, 2H), 1.82 (t, J = 11.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 145.1, 143.4, 95.4, 31.2, 26.5; MS (EI, 70 eV) m/z: 154.18, 111.15, 97.15, 79.19; HRMS ESI (m/z): calcd for C7H11N2S [M + H]+: 155.0637, found: 155.0637. 8-Propyl-1,2,8-triazaspiro[4.5]deca-1,3-diene (3f). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (56.5 mg, 61%); IR (KBr): 2935, 1740, 1454, 1250, 780 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.62 (d, J = 3.3 Hz, 1H), 7.08 (d, J = 2.9 Hz, 1H), 3.08−2.99 (m, 2H), 2.66 (d, J = 4.8 Hz, 2H), 2.52−2.46 (m, 2H), 1.86−1.73 (m, 4H), 1.59 (dd, J = 15.2, 7.5 Hz, 2H), 0.95 (t, J = 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 145.1, 143.0, 95.1, 60.7, 51.8, 30.1, 20.1, 12.0; MS (EI, 70 eV) m/z: 179.32, 150.25, 122.22, 98.23; HRMS ESI (m/z): calcd for C10H18N3 [M + H]+: 180.1495, found: 180.1494. 8-Phenethyl-1,2,8-triazaspiro[4.5]deca-1,3-diene (3g). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (102.6 mg, 85%); IR (KBr): 3080, 2935, 1500, 1128, 763 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.63 (s, 1H), 7.30 (t, J = 7.3 Hz, 2H), 7.25−7.19 (m, 3H), 7.09 (s, 1H), 3.11 (t, J = 10.7 Hz, 2H), 2.94−2.86 (m, 2H), 2.80−2.74 (m, 4H), 1.87−1.76 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 145.0, 143.0, 140.1, 128.6, 128.3, 126.0, 94.8, 60.4, 51.6, 33.6, 30.0; MS (EI, 70 eV) m/z: 241.32, 150.26, 121.21, 91.16; HRMS ESI (m/z): calcd for C15H20N3 [M + H]+: 242.1652, found: 242.1655. Ethyl 1,2,8-Triazaspiro[4.5]deca-1,3-diene-8-carboxylate (3h). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown oil (79.5 mg, 76%); IR (KBr): 2936, 1692, 1435, 1246, 774 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.63 (s, 1H), 7.01 (s, 1H), 4.16 (q, J = 7.0 Hz, 2H), 3.95− 3.79 (m, 4H), 1.73−1.65 (m, 2H), 1.57 (d, J = 13.5 Hz, 2H), 1.26 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 155.5, 144.5, 143.5, 94.5, 61.5, 42.3, 29.7, 14.6; MS (EI, 70 eV) m/z: 209.28, 180.24, 120.21, 108.20; HRMS ESI (m/z): calcd for C10H15N3NaO2 [M + Na]+: 232.1056, found: 232.1055. 1,2-Diazaspiro[4.6]undeca-1,3-diene (3i). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a black oil (42.8 mg, 57%); IR (KBr): 2924, 2857, 1692, 1450, 1246 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.46 (s, 1H), 7.08 (s, 1H), 2.08−1.97 (m, 4H), 1.82−1.58 (m, 6H), 1.33 (dd, J = 14.5, 8.5 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 146.8, 142.0, 100.4, 32.1, 29.4, 25.6; MS (EI, 70 eV) m/z: 150.26, 121.20, 107.20, 94.21; HRMS ESI (m/z): calcd for C9H14N2Na [M + Na]+: 173.1049, found: 173.1042. 1,2-Diazaspiro[4.7]dodeca-1,3-diene (3j). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1), the product was isolated as a brown oil (56.7 mg, 69%); IR (KBr): 3095, 2924, 1598, 1454, 774 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.54 (d, J = 1.9 Hz, 1H), 7.10 (d, J = 1.7 Hz, 1H), 2.05 (dd, J = 13.6, 8.8 Hz, 2H), 1.96 (dd, J = 13.7, 11.6 Hz, 2H), 1.87−1.58 (m, 8H), 1.33 (dd, J = 14.8, 8.3 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 146.9, 142.6, 100.3, 28.3, 28.2, 25.0, 24.9; MS (EI, 70 eV) m/z: 164.28, 135.24, 121.21, 107.18; HRMS ESI (m/z): calcd for C10H16N2Na [M + Na]+: 187.1206, found: 187.1205. (1r,3r,5r,7r)-Spiro[adamantane-2,3′-pyrazole] (3k). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 20:1),

the product was isolated as a yellow crystalline solid (75.3 mg, 80%), mp 104.0−105.2 °C; IR (KBr): 3093, 2901, 1738, 1446, 1241, 779 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.56 (s, 1H), 7.34 (s, 1H), 2.83 (d, J = 12.6 Hz, 2H), 2.10 (d, J = 45.4 Hz, 2H), 1.90 (dd, J = 36.2, 17.8 Hz, 8H), 1.33 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 145.6, 142.3, 102.0, 38.6, 37.7, 37.5, 35.7, 35.3, 35.2, 31.4, 27.3, 27.2; MS (EI, 70 eV) m/z: 188.28, 131.20, 117.23, 91.18; HRMS ESI (m/z): calcd for C12H16N2Na [M + Na]+: 211.1206, found: 211.1210. 4,5,6,7-Tetrahydro-2H-indazole (3l). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a yellow oil (34.2 mg, 56%); IR (KBr): 3163, 2930, 1445, 1157, 960 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.61 (s, 1H), 7.29 (s, 1H), 2.66 (t, J = 6.0 Hz, 2H), 2.53 (t, J = 5.9 Hz, 2H), 1.84− 1.70 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 143.2, 132.0, 115.0, 23.4, 23.1, 22.0, 20.4; MS (EI, 70 eV) m/z: 122.23, 119.20, 94.20, 67.18; HRMS ESI (m/z): calcd for C7H11N2 [M + H]+: 123.0917, found: 123.0914. 4,5,6,7-Tetramethyl-6,7-dihydro-2H-indazole (4a). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a yellow oil (45.0 mg, 51%); IR (KBr): 3217, 2963, 1728, 1376, 1058 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.29 (s, 1H), 5.12 (dr, 1H), 2.81−2.68 (m, 1H), 2.12−1.81 (m, 1H), 1.91 (s, 3H), 1.81 (s, 3H), 1.10 (d, J = 7.1 Hz, 3H), 0.94 (d, J = 7.1 Hz, 3H); 13 C NMR (100 MHz, CDCl3) δ 150.5, 129.1, 123.8, 118.1, 117.6, 44.4, 34.2, 20.8, 18.6, 18.0, 14.7; MS (EI, 70 eV) m/z: 176.30, 161.27, 146.23, 131.20; HRMS ESI (m/z): calcd for C11H17N2 [M + H]+: 177.1386, found: 177.1379. Anal. Calcd for C11H16N2: C, 74.96; H, 9.15; N, 15.89; Found: C, 75.10; H, 9.22; N, 15.68. 4,5-Dihydro-2H-benzo[e]indazole (4b). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown amorphous solid (57.8 mg, 68%), mp 127.1− 128.0 °C; IR (KBr): 3172, 2931, 1592, 1176, 761 cm−1; 1H NMR (400 MHz, CDCl3) δ 11.12 (dr, 1H), 7.78 (s, 1H), 7.39 (d, J = 7.4 Hz, 1H), 7.20 (t, J = 7.3 Hz, 2H), 7.10 (t, J = 7.3 Hz, 1H), 2.97 (dd, J = 19.7, 6.5 Hz, 4H); 13C NMR (100 MHz, CDCl3) δ 146.5, 134.1, 130.3, 128.4, 126.8, 126.6, 125.8, 122.8, 117.2, 29.5, 21.2; MS (EI, 70 eV) m/z: 170.10, 142.08, 115.06, 84.10; HRMS ESI (m/z): calcd for C11H11N2 [M + H]+: 171.0917, found: 171.0914. 8-Methyl-4,5-dihydro-2H-benzo[e]indazole (4c). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown amorphous solid (56.2 mg, 61%), mp 172.5−173.2 °C; IR (KBr): 3180, 2929, 1725, 1164, 810 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.77 (s, 1H), 7.23 (s, 1H), 7.11 (d, J = 7.6 Hz, 1H), 6.93 (d, J = 7.6 Hz, 1H), 3.00−2.89 (m, 4H), 2.34 (s, 3H); 13 C NMR (100 MHz, CDCl3) δ 146.8, 136.3, 131.1, 130.0, 129.5, 128.2, 126.5, 123.5, 117.3, 29.1, 21.3, 21.1; MS (EI, 70 eV) m/z: 184.26, 169.24, 142.22, 115.20; HRMS ESI (m/z): calcd for C12H13N2 [M + H]+: 185.1073, found: 185.1075. 8-Chloro-4,5-dihydro-2H-benzo[e]indazole (4d). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown amorphous solid (52.1 mg, 51%), mp 144.1−145.6 °C; IR (KBr): 3164, 2930, 1595, 1170, 805 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.78 (s, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.14 (d, J = 8.1 Hz, 1H), 7.10−6.90 (m, 2H), 3.06−2.84 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 147.1, 132.4, 132.4, 131.9, 129.6, 128.0, 125.6, 122.8, 116.6, 29.0, 21.1; MS (EI, 70 eV) m/z: 204.22, 169.25, 140.20, 115.21; HRMS ESI (m/z): calcd for C11H10ClN2 [M + H]+: 205.0527, found: 205.0525. 7-Fluoro-4,5-dihydro-2H-benzo[e]indazole (4e). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown amorphous solid (48.9 mg, 52%), mp 76.2−77.3 °C; IR (KBr): 3180, 2931, 1579, 1243, 812 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.74 (s, 1H), 7.34 (dd, J = 8.3, 5.6 Hz, 1H), 6.96−6.89 (m, 2H), 4.58 (dr, 1H), 3.11−2.84 (m, 4H); 13C NMR 9483

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

Article

The Journal of Organic Chemistry (100 MHz, CDCl3) δ 161.1 (J = 242.7 Hz), 146.3, 136.4 (J = 7.4 Hz), 126.4 (J = 2.8 Hz), 126.1, 124.0 (J = 8.1 Hz), 116.6, 115.4 (J = 21.5 Hz), 113.4 (J = 21.4 Hz), 29.7 (J = 1.2 Hz), 20.9; MS (EI, 70 eV) m/z: 188.24, 160.20, 133.20, 93.61; HRMS ESI (m/z): calcd for C11H10FN2 [M + H]+: 189.0823, found: 189.0822. Anal. Calcd for C11H9FN2: C, 70.20; H, 4.82; N, 14.88; Found: C, 70.41; H, 4.92; N, 14.71. 7-Bromo-4,5-dihydro-2H-benzo[e]indazole (4f). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a white amorphous solid (69.5 mg, 56%), mp 103.4−105.1 °C; IR (KBr): 3181, 2933, 1726, 1066, 811 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.70 (s, 1H), 7.37−7.22 (m, 2H), 7.23− 7.02 (m, 2H), 2.93−2.83 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 146.3, 136.1, 131.2, 129.7, 129.2, 126.7, 124.2, 118.9, 116.4, 29.3, 20.9; MS (EI, 70 eV) m/z: 248.17, 169.24, 140.19, 115.20; HRMS ESI (m/ z): calcd for C11H10BrN2 [M + H]+: 249.0022, found: 249.0016. Anal. Calcd for C11H9BrN2: C, 53.04; H, 3.64; N, 11.25; Found: C, 53.19; H, 3.70; N, 11.13. 4,5,8,10-Tetrahydro-2H-isobenzofuro[4,5-e]indazole (4g). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 3:1), the product was isolated as a brown amorphous solid (60.5 mg, 57%), mp 161.3−161.9 °C; IR (KBr): 3739, 2923, 1463, 1239, 807 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.66 (s, 1H), 7.00 (d, J = 8.0 Hz, 1H), 6.59 (d, J = 8.0 Hz, 1H), 5.89 (dr, 1H), 4.65 (t, J = 8.7 Hz, 2H), 3.28 (t, J = 8.6 Hz, 2H), 3.05−2.87 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 159.2, 147.6, 127.7, 127.7, 126.9, 126.2, 121.4, 116.3, 106.3, 30.0, 29.0, 21.8, 21.8; MS (EI, 70 eV) m/z: 212.28, 184.24, 156.23, 91.18; HRMS ESI (m/z): calcd for C13H13N2O [M + H]+: 213.1022, found: 213.1024. 2,6,7,8-Tetrahydrocyclohepta[c]pyrazole (4h). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (45.6 mg, 68%); IR (KBr): 3217, 2930, 1713, 1437, 1144, 807 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.37 (s, 1H), 6.49 (dr, 1H), 6.22 (d, J = 11.5 Hz, 1H), 5.68− 5.57 (m, 1H), 3.00−2.90 (m, 2H), 2.47−2.42 (m, 2H), 1.94 (dt, J = 11.4, 5.7 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 146.3, 129.9, 128.8, 127.2, 119.1, 31.2, 28.1, 22.8; MS (EI, 70 eV) m/z: 134.25, 119.20, 92.18, 79.18; HRMS ESI (m/z): calcd for C8H11N2 [M + H]+: 135.0917, found: 135.0910. Anal. Calcd for C8H10N2: C, 71.61; H, 7.51; N, 20.88; Found: C, 71.87; H, 7.54; N, 20.59. 6,6-Dimethyl-2,6,7,8-tetrahydrocyclohepta[c]pyrazole (4i). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a yellow oil (64.1 mg, 79%); IR (KBr): 3649, 2934, 1727, 1457, 800 cm−1; 1H NMR (400 MHz, CDCl3) δ 10.49 (dr, 1H), 7.38 (s, 1H), 6.08 (d, J = 11.7 Hz, 1H), 5.40 (d, J = 11.7 Hz, 1H), 2.97−2.87 (m, 2H), 1.79−1.69 (m, 2H), 1.09 (s, 6H); 13C NMR (100 MHz, CDCl3) δ 145.6, 137.2, 134.7, 116.9, 115.8, 36.8, 35.8, 30.1, 22.7; MS (EI, 70 eV) m/z: 162.26, 147.24, 19.20, 92.20; HRMS ESI (m/z): calcd for C10H15N2 [M + H]+: 163.1230, found: 163.1230. 2,4,5,6-Tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4j). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a black oil (60.7 mg, 66%); IR (KBr): 3066, 2935, 1601, 1440, 759 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.65 (d, J = 3.3 Hz, 1H), 7.27−7.16 (m, 3H), 6.96 (t, J = 7.4 Hz, 1H), 6.20 (d, J = 7.8 Hz, 1H), 3.11−2.96 (m, 2H), 2.45 (dt, J = 7.4, 6.5 Hz, 1H), 2.00 (dd, J = 14.7, 9.0 Hz, 2H), 1.79 (t, J = 10.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 147.6, 143.2, 137.6, 130.3, 128.2, 126.6, 126.0, 125.4, 98.6, 29.5, 29.5, 21.9; MS (EI, 70 eV) m/z: 184.09, 169.06, 128.06, 115.07; HRMS ESI (m/z): calcd for C12H13N2 [M + H]+: 185.1073, found: 185.1070. 9-Methoxy-2,4,5,6-tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4k). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a black oil (90.0 mg, 84%); IR (KBr): 3096, 2936, 1605, 1497, 1244, 1036 cm−1;

H NMR (400 MHz, CDCl3) δ 7.65 (d, J = 3.3 Hz, 1H), 7.16 (dd, J = 8.3, 5.9 Hz, 2H), 6.78 (dd, J = 8.5, 2.7 Hz, 1H), 5.71 (d, J = 2.6 Hz, 1H), 3.61 (s, 3H), 2.96 (tdd, J = 11.6, 9.2, 4.5 Hz, 2H), 2.46−2.37 (m, 1H), 2.05−1.94 (m, 2H), 1.77 (dd, J = 15.9, 5.9 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 157.6, 147.6, 143.1, 131.1, 129.6, 127.4, 114.8, 109.7, 98.7, 55.1, 29.4, 28.7, 22.1; MS (EI, 70 eV) m/z: 214.30, 199.26, 183.25, 156.22; HRMS ESI (m/z): calcd for C13H15N2O [M + H]+: 215.1179, found: 215.1178. 9-Chloro-2,4,5,6-tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4l). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a black oil (79.7 mg, 73%); IR (KBr): 3094, 2939, 1590, 1479, 807 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.68 (d, J = 3.3 Hz, 1H), 7.15 (dd, J = 6.7, 3.2 Hz, 3H), 6.18 (s, 1H), 3.09−2.91 (m, 2H), 2.44 (dt, J = 17.6, 7.6 Hz, 1H), 2.03−1.96 (m, 2H), 1.80 (dd, J = 18.3, 8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 147.0, 143.7, 136.0, 131.5, 131.5, 128.4, 128.4, 125.3, 98.1, 29.2, 29.0, 21.7; MS (EI, 70 eV) m/z: 218.24, 183.27, 156.25, 127.20; HRMS ESI (m/z): calcd for C12H12ClN2 [M + H]+: 219.0684, found: 219.0682. 8-Methoxy-2,4,5,6-tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4m). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a black amorphous solid (84.6 mg, 79%), mp 150.3−151.2 °C; IR (KBr): 2934, 1602, 1254, 1038, 822 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.62 (d, J = 3.3 Hz, 1H), 7.13 (d, J = 3.3 Hz, 1H), 6.75 (d, J = 2.5 Hz, 1H), 6.54 (dd, J = 8.6, 2.6 Hz, 1H), 6.14 (d, J = 8.6 Hz, 1H), 3.75 (s, 3H), 3.09−2.94 (m, 2H), 2.50−2.37 (m, 1H), 2.04−1.93 (m, 2H), 1.85−1.76 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 159.3, 147.6, 142.9, 139.1, 123.6, 118.5, 114.6, 112.5, 98.2, 55.1, 29.9, 29.5, 21.9; MS (EI, 70 eV) m/z: 214.28, 199.25, 171.23, 130.22; HRMS ESI (m/z): calcd for C13H15N2O [M + H]+: 215.1179, found: 215.1175. 8,9-Dimethoxy-2,4,5,6-tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4n). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 3:1), the product was isolated as a brown oil (107.5 mg, 88%); IR (KBr): 3337, 2934, 1737, 1513, 1253, 1034 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 3.3 Hz, 1H), 7.15 (d, J = 3.3 Hz, 1H), 6.69 (s, 1H), 5.62 (s, 1H), 3.84 (s, 3H), 3.62 (s, 3H), 3.04−2.88 (m, 2H), 2.45−2.36 (m, 1H), 2.04−1.93 (m, 2H), 1.74 (dd, J = 13.1, 6.7 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 149.0, 147.8, 147.3, 142.9, 130.2, 118.0, 112.4, 107.6, 98.4, 55.7, 55.7, 29.4, 29.2, 22.1; MS (EI, 70 eV) m/z: 244.30, 229.28, 201.27, 160.23; HRMS ESI (m/z): calcd for C14H17N2O2 [M + H]+: 245.1285, found: 245.1290. 4-Methyl-2,4,5,6-tetrahydrobenzo[3,4]cyclohepta[1,2-c]pyrazole (4o). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a yellow oil (61.5 mg, 62%); IR (KBr): 3190, 2935, 1730, 1453, 949, 754 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.60 (d, J = 7.1 Hz, 1H), 7.45 (s, 1H), 7.21−7.12 (m, 3H), 6.28 (dr, 1H), 3.09−2.86 (m, 1H), 2.81−2.62 (m, 2H), 2.19−2.01 (m, 1H), 1.70−1.56 (m, 1H), 1.22 (d, J = 6.9 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 141.6, 136.0, 130.2, 129.5, 127.7, 127.0, 126.4, 125.9, 123.5, 36.3, 33.0, 30.3, 22.9; MS (EI, 70 eV) m/z: 198.28, 183.27, 168.24, 115.21; HRMS ESI (m/z): calcd for C13H15N2 [M + H]+: 199.1230, found: 199.1233. 4,5-Dihydro-2H-benzo[6,7]oxepino[4,5-c]pyrazole (4p). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a black oil (49.4 mg, 53%); IR (KBr): 3093, 2962, 1486, 1228, 761 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.72 (d, J = 3.3 Hz, 1H), 7.20 (t, J = 7.7 Hz, 1H), 7.12 (d, J = 3.3 Hz, 1H), 6.98 (d, J = 8.3 Hz, 1H), 6.72 (t, J = 7.5 Hz, 1H), 6.25 (d, J = 7.8 Hz, 1H), 4.82 (td, J = 11.0, 2.4 Hz, 1H), 4.43 (ddd, J = 11.2, 4.9, 3.6 Hz, 1H), 2.23 (ddd, J = 13.8, 10.2, 3.4 Hz, 1H), 1.89 (ddd, J = 14.0, 5.1, 2.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 155.3, 145.4, 144.4, 130.1, 126.1, 120.6, 118.2, 112.8, 94.2, 61.5, 27.7; MS (EI, 70 eV) m/z: 1

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DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

Article

The Journal of Organic Chemistry Notes

186.26, 171.23, 128.21, 115.20; HRMS ESI (m/z): calcd for C11H11N2O [M + H]+: 187.0866, found: 187.0866. 4,5,6,7-Tetrahydro-2H-benzo[3,4]cycloocta[1,2-c]pyrazole (4q). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (49.5 mg, 50%); IR (KBr): 3320, 2922, 2861, 1732, 754 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.57 (d, J = 3.3 Hz, 1H), 7.51 (d, J = 3.4 Hz, 1H), 7.21−7.13 (m, 2H), 7.01 (ddd, J = 19.0, 10.4, 5.1 Hz, 2H), 3.19 (ddd, J = 24.5, 14.5, 9.1 Hz, 2H), 2.41−2.18 (m, 2H), 2.01−1.42 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 144.0, 143.1, 142.1, 136.2, 130.9, 128.0, 126.4, 126.1, 102.5, 36.6, 34.4, 31.0, 27.8; MS (EI, 70 eV) m/z: 198.13, 183.12, 169.10, 142.10; HRMS ESI (m/z): calcd for C13H15N2 [M + H]+: 199.1230, found: 199.1228. (R)-8-Methyl-5-(prop-1-en-2-yl)-2,4,5,6-tetrahydrocyclohepta[c]pyrazole (6). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (73.4 mg, 78%); IR (KBr): 2908, 1730, 1657, 1047 cm−1; 1H NMR (400 MHz, CDCl3) δ 9.81 (dr, 1H), 7.45 (s, 1H), 5.46 (t, J = 5.3, 5.3 Hz, 1H), 4.73 (s, 2H), 3.11−2.88 (m, 2H), 2.52 (ddd, J = 10.0, 7.8, 2.6 Hz, 1H), 2.48−2.38 (m, 2H), 2.01 (d, J = 1.2 Hz, 3H), 1.77 (s, 3H); 13 C NMR (100 MHz, CDCl3) δ 149.6, 144.3, 132.5, 126.2, 122.9, 119.4, 109.3, 41.2, 36.1, 33.4, 23.1, 20.5; MS (EI, 70 eV) m/z: 188.30, 173.28, 147.24, 131.21; HRMS ESI (m/z): calcd for C12H17N2 [M + H]+: 189.1386, found: 189.1383. [α]D20 = 37.7 (c 0.945, CH2Cl2). (5S,5aR,7S)-5,5a-Dimethyl-7-(prop-1-en-2-yl)-2,4,5,5a,6,7,8,9octahydrobenzo[5,6]cyclohepta[1,2-c]pyrazole (8). The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 10:1), the product was isolated as a brown oil (57.6 mg, 45%); IR (KBr): 3164, 2933, 1733, 1447, 884 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.81 (dr, 1H), 7.32 (s, 1H), 6.07 (s, 1H), 4.71 (s, 2H), 2.92−2.72 (m, 2H), 2.60−2.19 (m, 4H), 1.93−1.72 (m, 5H), 1.32−1.24 (m, 2H), 1.14−0.98 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 150.2, 146.8, 143.6, 132.5, 116.9, 112.8, 108.7, 45.7, 43.3, 41.0, 40.9, 37.0, 33.6, 30.8, 20.8, 19.5, 17.6; MS (EI, 70 eV) m/z: 256.18, 213.15, 187.12, 145.10; HRMS ESI (m/z): calcd for C17H25N2 [M + H]+: 257.2012, found: 257.2011. Anal. Calcd for C17H24N2: C, 79.64; H, 9.44; N, 10.92; Found: C, 79.98; H, 9.34; N, 10.68. [α]D20 = 85.3 (c 0.842, CH2Cl2). D2-4m. The title compound was prepared via the general procedure. After purification by silica gel column chromatography (petroleum ether:EtOAc = 5:1), the product was isolated as a brown oil (86.5 mg, 80%); IR (KBr): 2932, 1600, 1494, 1248, 1032 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.62 (s, 0.03H), 7.13 (s, 0.03H), 6.75 (d, J = 2.7 Hz, 1H), 6.54 (dd, J = 8.6, 2.8 Hz, 1H), 6.14 (d, J = 8.6 Hz, 1H), 3.75 (s, 3H), 3.11−2.89 (m, 2H), 2.54−2.36 (m, 1H), 2.10−1.88 (m, 2H), 1.86−1.70 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 159.3, 147.2 (J = 27.1 Hz), 142.6 (J = 28.5 Hz), 139.1, 126.6, 118.5, 114.6, 112.5, 98.1, 55.1, 29.9, 29.5, 21.9; MS (EI, 70 eV) m/z: 216.31, 215.29, 200.24, 116.19; HRMS ESI (m/z): calcd for C13H12D2N2O [M + H]+: 216.1226, found: 216.1230.

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Key Research and Development Program of China (Grant 2016YFA0602900), the National Natural Science Foundation of China (Grants 21490572 and 21420102003), and the Pearl River S&T Nova Program of Guangzhou (Grant 201610010160).

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01496. Crystal structure determination and copies of 1H and 13C NMR spectra for all new products (PDF) X-ray crystal structure of compound 3b (CIF)

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Huanfeng Jiang: 0000-0002-4355-0294 9485

DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486

Article

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DOI: 10.1021/acs.joc.7b01496 J. Org. Chem. 2017, 82, 9479−9486